Polyamides, known commercially as nylons, have excellent hardness, abrasion resistance, chemical resistance and other mechanical properties, but suffer from being brittle. Many attempts have been made to make polyamides less brittle by blending the polyamides with impact modifiers such as rubbery polymers. U.S. Pat. No. 4,174,358 discloses the use of functionalized rubbers as impact modifiers for polyamides. U.S. Pat. Nos. 4,427,828 and 4,628,072 disclose the use of acid functionalized, hydrogenated block copolymers of styrene and conjugated diolefins as impact modifiers for polyamides, and U.S. Pat. No. 4,427,828 additionally discloses the use of functionalized hydrogenated homopolymers of conjugated diolefins. The inclusion of polar functional groups on the modifiers is generally considered to be necessary for the polyamides to be acceptably compatible with rubbers which do not otherwise contain polar functionality.
The use of the acid derivative functionalized, hydrogenated styrenic block copolymers or acid derivative functionalized, hydrogenated conjugated diolefin homopolymers as impact modifiers is particularly effective in modifying polyamides which are prepared by copolymerizing diamines and dicarboxylic acids, such as nylon 6-6. When these polyamides are modified with acid derivative functionalized, hydrogenated block copolymers of styrene and butadienes, compositions may be made which fail in the ductile mode rather than the brittle mode when 1/8 inch notched Izod impact toughness is tested by ASTM-D256. Further, with a sufficient amount of modifier the ductile failure will remain at temperatures which are as low as -20.degree. F.
Polyamides which are prepared by polymerizing monoaminocarboxylic acids or internal lactame thereof, such as nylon 6, are more difficult to toughen with acid functionalized hydrogenated polymers of conjugated diolefins or copolymers of conjugated diolefins and vinyl aromatics. Polyamides prepared by polymerizing monoaminocarboxylic acids or their internal lactams have an amine functional group at one terminal and a carboxyl group at the other terminal. Nylons prepared by copolymerizing diamines and dicarboxylic acid generally performed in an excess of diamines. When the polymerization is not carried out with an excess of diamines, polyamides such as these will be a combination of polymer molecules having two terminal amines, two terminal carboxylic acids, and one of each terminal groups. The two types of nylons, because of this difference in terminal functionality, have inherently different compatibilities with functionalized polymeric modifiers. The functionalized polymers are significantly more compatible with nylon 6 than they are with nylon 6-6. Because of this difference in compatibility, acid derivative functionalized, hydrogenated polyconjugated diolefins will form smaller domains when mixed with nylon 6 than when mixed with nylon 6-6 in conventional mixing devices. The particle size of modifier in nylons greatly effects the effectiveness of the toughening modifier. As a result, functionalized polymers are not as effective as toughening modifiers in nylon 6 as they are in nylon 6-6.
Nylon 6-6 compositions may be made by high shear blending of functionalized hydrogenated block copolymers of styrene and butadiene with the nylon 6-6 which exhibit ductile failure rather than brittle failure in a 1/8" notched Izod impact toughness test, at temperatures at or below -20.degree. F. About 20 weight percent modifier is required to achieve this result. Nylon 6, on the other hand, requires much more modifier to achieve ductile failure at -20.degree. F. The higher levels of modifier are undesirable because they result in a less stiff composition, sacrificing more of the excellent properties of the nylon. The lack of stiffness is indicated by a modulus which is low. This can be undesirable for many applications.
Polyamides which have carboxylic acid, or a derivative thereof as one terminal group and an amine as another terminal group will be referred to generally as .alpha.-polyamides. These .alpha.-polyamides may be formed by ring-opening of lactams and polymerization of monoaminocarboxylic acids.
It is therefore an object of this invention to provide a process to blend .alpha.-polyamides with acid derivative functionalized hydrogenated conjugated diolefin polymers which result in improved toughness of the resulting composition. In another aspect, it is an object to provide a modified .alpha.-polyamide composition comprising 20 parts by weight or less of modifier for each 80 parts by weight .alpha.-polyamide, the composition exhibiting ductile failure in a 1/8" notched Izod toughness test at -20.degree. F., the modifier being an acid derivative functionalized hydrogenated conjugated diolefin polymer.